Ink jet printing has become a prominent contender in the digital output arena because of its non-impact, low-noise characteristics and its compatibility with plain paper. Ink jet printings avoids the complications of toner transfers and fixing as in electrophotography and the pressure contact at the printing interface as in thermal resistive printing technologies. Ink jet printing mechanisms includes continuous ink jet and drop-on-demand ink jet. U.S. Pat. No. 3,946,398, which issued to Kyser et al. in 1970, discloses a drop-on-demand ink jet printer which applies a high voltage to a piezoelectric crystal, causing the crystal to bend, applying pressure on an ink reservoir and jetting drops on demand. Piezoelectric ink jet printers can also utilize piezoelectric crystals in push mode, shear mode, and squeeze mode. EP 827 833 A2 and WO 98/08687 disclose a piezoelectric ink jet print head apparatus with reduced crosstalk between channels, improved ink protection, and capability of ejecting variable ink drop size.
U.S. Pat. No. 4,723,129 issued to Endo et al discloses an electrothermal drop-on-demand ink jet printer which applies a power pulse to an electrothermal heater which is in thermal contact with water based ink in a nozzle. A small quantity of ink rapidly evaporates, forming a bubble which causes an ink drop to be ejected from small apertures along the edge of the heater substrate. This technology is known as Bubblejet.TM. (trademark of Canon K.K. of Japan).
U.S. Pat. No. 4,460,728, which issued to Vaught et al. in 1982, discloses an electrothermal drop ejection system which also operates by bubble formation to eject drops in a direction normal to the plane of the heater substrate. As used herein, the term "thermal ink jet" is used to refer to both this system and system commonly known as Bubblejet.TM..
Ink jet nozzles are an essential component in an ink jet printer. The shapes and dimensions of the ink jet nozzles strongly affect the properties of the ink drops ejected from that ink jet nozzle. For example, it is well known in the art that if the diameter of the ink jet nozzle opening deviates from the desired size, both ink drop volume and the velocity can vary from the desired values. In another example, if the opening of an ink jet nozzle is formed with an irregular shape, the trajectory of the ejected ink drop from that ink jet nozzle can also deviate from the desired direction (usually normal to the plane of the nozzle plate).
One method of forming ink jet nozzle plates is the electroforming process. Such a process uses a mandrel overcoated with a continuous conductive film patterned and non-conductive structures that protrude over the conductive film. A metallic nozzle plate is formed using such a mandrel by electroplating on the conductive film. Over time, the metallic layer grows in thickness. The ink jet nozzles are defined by the non-conductive structures.
One known problem in the above-described prior art is in the variability of the diameter of the ink jet nozzles. The growth rate of the metallic layer can vary at different areas of the mandrel in the electroforming process as well as between different batches. The growth rate variability results in variability in the size of the openings as defined by the edge of the growth front of the metallic layer. This problem is particularly severe for forming ink jet nozzles with small diameters. A slight variability in the growth rate of the metallic layer in the electroplating process will result in a large relative error in the nozzle diameter.
Another need for ink jet nozzles in an ink jet printing apparatus is to optimize the shape of ink jet nozzle exit and the ink funnel that feed the ink fluid to the ink jet nozzles. It is known that the ink funnel can exist in cone, cylindrical, or toroidal shapes. The ink jet nozzle can be round, square or triangular. The structural designs of the ink jet nozzles and ink funnels strongly influence the dynamics of the ink fluid during ink drop ejection, and therefore determine to a large extent the properties of the ejected ink drop.